The proposed experiments incorporte two heretofore separate but highly productive lines of attack on defining and elucidating the neural substrate of memory, a problem of vast import to fields as diverse as education, psychiatry, neurology and gerontology. The experiments utilize, on the one hand, the sophisticated techniques recently developed for testing memory in nonhuman primates. These have demonstrated a striking similarity between macque and man in the processes of visual memory, both in its normal operation and in the nature of the impairment consequent to homologous cerebral loss. On the other hand, these experiments exploit the extraordinary possibilities afforded by the "split-brain" approach, whereby information can be supplied to or demanded from each cerebral hemisphere individually, thus allowing comparison of performance by "intact" versus damaged hemispheres in the same animal, the tracing and comparison of different pathways for interhemispheric communication, etc. Macaques with surgically transected optic chiasm view with one or the other eye, or each seriatim, a number of pictures which they are subsequently called upon to identify when viewed by the same or other eye and hemisphere. Interhemispheric communication is limited by cutting one of the forebrain commissures. Lesions are to be created reversibly by cooling, local anesthetization, or electrical tetanization; and irreversibly by subpial suction or transection. The primary goals are to study 1) how initial distribution of visual mnemonic input to one or the other hemisphere affects the retrieval of these memories when achieved ipsilaterally, contralaterally or bilaterally, comparing interhemishpheric communication via anterior commissure versus splenium of the corpus callosum in this regard; and 2) to define how unilateral, reversible or irreversible, elimination of various cerebral structures having a suspected role in visual memory will alter the mnemonic capability of that hemisphere, particulary as to whether "recording" versus "retrieval" is differentially affected. By such means, it should be possible to define the structures essential to visual mnemonic processing, and to some degree the nature of their role therein.